JPH0257249B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an air amount measuring sensor of an internal combustion engine, and more specifically, to shortening the current flowing through a hot wire used in a constant temperature anemometer as an air amount measuring sensor in accordance with an operating characteristic quantity. The present invention relates to a control device for an air amount measuring sensor of an internal combustion engine for controlling a scorching process in which a heating wire is scorched by increasing the time.

German Patent Publication No. 2750050 describes an air volume measuring sensor that operates according to the principle of a constant temperature anemometer, the hot wire of which is scorched after each measuring cycle to eliminate impurities deposited on it. is being burnt down. This hot wire scorching is accomplished in conventional equipment by unbalancing the bridge circuit and thereby causing a large current to flow.
Therefore, the hot wire is subjected to a large load during the scorching process. In order to reduce such loads, it has been proposed to reduce the number of scorching steps, e.g. scorching or burning out only after a predetermined number of cycles rather than after each measurement cycle. I have to. Although such conventional devices usually provide good results, various problems occur in actual driving.

To burn off the residue attached to the hot wire, e.g.
It is carried out at a temperature of 1050°C and lasts for about 1 second. After the end of the measurement cycle, ie when the internal combustion engine is stopped, a burn-out step takes place, which, if the engine is warm, will ignite the fuel vapors rising up the intake pipe. As a result, an independent temperature rise occurs in the hot wire that cannot be checked and may even destroy the hot wire.

Therefore, the present invention solves these conventional drawbacks and provides an internal combustion engine that can reliably control the scorching process even in the event of an independently generated temperature rise of the hot rays that cannot be checked. An object of the present invention is to provide a control device for an air amount measuring sensor.

According to the present invention, the temperature rise that occurs uniquely due to the special ignition of the fuel vapor or the combustion of the air-fuel mixture is measured, and if such a temperature rise occurs, the burning process is interrupted.

In this way, according to the invention, the ignition of fuel vapor that occurs around the hot wire is detected and corresponding measures are taken accordingly, so that the hot wire can be used for a long time without being destroyed. This has the advantage of being possible.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a schematic diagram of the intake pipe of an internal combustion engine of the type that compresses the air-fuel mixture. There is. In detail, the intake pipe 10
A hot wire 12 of an air amount measuring sensor is arranged above the injection valve 11. This air amount measuring sensor is a sensor that operates according to the principle of a constant temperature anemometer. The injection valve 11 injects fuel in the region of the throttle valve 13, and the air-fuel mixture produced thereby is supplied to the individual cylinders (not shown) via the end 14 of the intake pipe facing the internal combustion engine.

In the embodiment shown in FIG. 1, the hot wire 12 is disposed inside the intake pipe 10, but it is also conceivable to store the hot wire in a bypass path to further reduce the amount of contamination of the hot wire.

In the embodiment shown in FIG. 1, a problem arises in that the air-fuel mixture in the intake pipe spontaneously ignites.
That is, after the end of each measurement cycle, i.e. after the internal combustion engine has stopped, if the previous mixture components have not been drawn in through the cylinder, the warm walls of the intake pipe cause the fuel vapor to There is a risk that the temperature will rise and reach the area of the hot wire 12. When this heat ray is scorching, that is, the temperature is raised to over 1000 degrees Celsius for burning out,
There is a danger that this gasoline vapor will ignite and destroy the heating wire.

FIG. 2 shows a typical curve of current flowing through a scorching hot wire. At the beginning of scorching, the current rises rapidly to its maximum value, then falls in a linear fashion,
It then decreases rapidly and remains at a predetermined value until the end of the burn. tf indicates burning time. It is known that a change in this current curve occurs when the air-fuel mixture undergoes a special ignition. The present invention detects this change and controls the burning process accordingly.

In the example illustrated in FIG. 2, two changes are noticeable. The first change is that the period of relatively large current flowing through the hot wire is shortened (see 1). The second change is that the burning current decreases below a certain value (see 2).

The control device according to the invention detects this current change and performs control to cut off the scorching heat.

Previous knowledge has shown that the large current drop caused by the independent ignition of a scorching mixture is the easiest to measure. A flowchart for this is illustrated in FIG. After the firing process starts (step 20), the firing period tf is set (step 21). Next, burning begins (step 22), and a predetermined current flows through the hot wire (step 22).
23), this current is detected as a voltage, for example via a measuring resistor. If the current flowing through the hot wire is above a predetermined threshold (step 24), the burning process continues for a set time tf. On the other hand, if the current flowing through the hot wire is less than a predetermined value (which is equivalent to a decrease in voltage), it is assumed that a specific ignition has occurred and the scorching The process is finished.

Thus, in the case of FIG. 3A, the current flowing through the hot wire is detected and processed to determine whether an independent ignition of the air-fuel mixture has taken place.

On the other hand, in the case of the flowchart shown in Figure 3B,
At the start of scorching, we measure the period ta during which a relatively large current flows through the hot wire. If a unique ignition occurs, the period ta will be shorter compared to the case without such ignition. In this way, by detecting the average value to, it is detected whether or not a unique ignition has occurred. If it occurs, the burning will be interrupted as well.

In view of the fact that the burning process is controlled using a computer, two flowcharts are illustrated in FIG. 3, and those skilled in the art can easily create a program based on these. .

An example of implementing the control device of the present invention using an analog circuit is shown in FIG. The circuit shown in the figure has two input terminals 30, 31, through which a pulse for starting the burning process is input. In addition, the second input terminal 31
A voltage signal Um indicating the current flowing through the hot wire is applied to . Connected after the terminal 30 is a first monostable multivibrator (MMV) 32, which is provided with a time control input terminal 33 and a reset terminal 34. The inverted output of this multivibrator 32 is connected via a resistor 35 to the base of a pnp transistor 36, whose emitter is connected to a positive line 37 and its collector is connected via a resistor 38 to ground. Output terminal 39 is connected to the collector of transistor 36.

The input terminal 31 is connected to the plus input terminal of the comparator 40, and the minus input terminal receives the voltage of a voltage divider made up of resistors 41 and 46 connected between the power supply lines. The output of the comparator 40 is connected to a second monostable multivibrator 42 via an inverter 43. Q of this multivibrator
The output is connected to the reset terminal 34 of the monostable multivibrator 32, and is reset by the output signal. This output is applied to the reset terminal of monostable multivibrator 42 via a voltage divider consisting of resistors 44 and 45.

Next, the operation of the circuit shown in FIG. 4 will be explained.

The pulse applied to terminal 30 activates the monostable multivibrator and its output decreases. As a result, the transistor 36 becomes conductive, and a positive potential is generated at the terminal 39. continue,
The current flowing through the hot wire is detected via the voltage signal Um applied to terminal 31. When this voltage is about 3.5 V or more, or the voltage applied to the scorching heat measurement resistor is about 0.3 V or less, the monostable multivibrator 42 is not triggered by the inverter 43, and as a result, the reset terminal 34 receives a reset signal. is not applied.

When the voltage Um at terminal 31 falls below a threshold value, monostable multivibrator 42 is triggered, thereby resetting multivibrator 32 and blocking transistor 36. As a result, the scorching is interrupted, so that the hot wire is prevented from being subjected to double loading due to the scorching process and to combustion of the mixture in the hot wire. It has been found that when the fuel is naturally ignited in this way, the life of the hot wire 12 can be significantly extended by interrupting the scorching process.

In FIG. 4, a signal is applied to the reset terminal of multivibrator 42 through resistor 44 in order to maintain the circuit in a predetermined state during periods other than the firing process.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the principle of the control device of the present invention, Fig. 2 is a diagram showing the characteristics of the current flowing through the hot wire, Figs. 3A and 3B are flowcharts explaining the operation, and Figs. FIG. 4 is a circuit diagram showing a circuit configuration for implementing the present invention using an analog circuit. 10... Intake pipe, 11... Injection valve, 12... Heat wire, 13... Throttle valve.

Claims (1)

[Scope of Claims] 1. A control device for an internal combustion engine air quantity measuring sensor for controlling a scorching process in which the current flowing in a hot wire used in the air quantity measuring sensor is increased for a short time based on an operating characteristic quantity to scorch the hot wire. 1. A control device for an air amount measuring sensor for an internal combustion engine, characterized in that a means for detecting a uniquely occurring temperature rise is provided, and the scorching process is controlled according to the detection result. 2. A control device for an air amount measuring sensor for an internal combustion engine according to claim 1, wherein the scorching process is controlled by detecting a current flowing through a hot wire or a voltage signal derived from the current. 3. A control device for an air amount measuring sensor for an internal combustion engine according to claim 2, wherein a target value and a current value of the current or voltage signal are compared during the scorching process. 4. The control device for an air amount measuring sensor for an internal combustion engine according to claim 3, wherein the comparison voltage value is set to about 3.5V or 0.3V for measurement during scorching heat. 5. A control device for an air amount measuring sensor for an internal combustion engine according to claim 1, which detects the time course of the current flowing through the hot wire or the voltage signal obtained therefrom to control the scorching process. 6. The control device for an air amount measuring sensor for an internal combustion engine according to claim 5, wherein the scorching process is cut off when the time period during which a relatively large current flows becomes smaller than a predetermined value. 7. A resettable time signal generator is actuated by the signal to start the burning process, and the time of the burning process is determined by the output signal thereof, and a comparison circuit 40 is provided to compare the current or voltage flowing through the hot wire, and the comparison signal is The control device for an air amount measuring sensor for an internal combustion engine according to any one of claims 1 to 4, wherein the time signal generator 32 is reset accordingly. 8. A control device for an air amount measuring sensor for an internal combustion engine according to claim 7, wherein another time signal generator 42 is disposed between the comparator 40 and the reset terminal 34 of the time signal generator 32. .